This invention relates to electromagnetic clutches, and more particularly to electromagnetic spring-wound clutches for use in refrigerant compressors for automotive air conditioners or other like devices.
Conventionally, a refrigerant compressor which is used in an automotive air conditioner is provided with an electromagnetic clutch which is arranged between the compressor and the output shaft of an automotive engine associated with the air conditioner to transmit torque from the engine to the compressor. Such an electromagnetic clutch is a spring-wound type comprising a driving member and a driven member axially aligned with each other for rotation about a common axis, a coil spring mounted around the driving and driven members for gripping engagement therewith and operatively connected at its one end to the driven member, and a clutch armature plate operatively connected to the other end of the coil spring. When the electromagnetic clutch is actuated, the clutch armature plate is drawn into frictional contact with a radial wall formed on the driving member due to electromagnetic force produced in an electromagnetic coil provided in the clutch, to cause the coil spring to be wound into gripping engagement with the driving and driven members to effect driving connection between the driving member and the driven member.
When the electromagnetic spring-wound clutch having the above arrangement is actuated when the engine is rotating at a high speed, large impact load is suddenly applied to the driven shaft of the refrigerant compressor, which can result not only in deformation or breakage of the component parts of the compressor body and the clutch, but also in the occurrence of noise caused by friction between the coil spring and the parts on which the coil is wound, as well as in abrasion in the coil spring and its associated parts.